Preparation method and application of alkali-acid synergistic modified biomass activated carbon

Abstract

The invention discloses a preparation method and application of alkali-acid synergistic modified biomass activated carbon, and belongs to the technical field of treatment of water environment polluted by refractory organic pollutants by using adsorbents. Waste biomass is used as a raw material to prepare biochar, and the biomass raw material is firstly subjected to alkali high-temperature activation and then subjected to acid hydrothermal activation to prepare the alkali-acid synergistic modified biomass activated carbon. The alkali-acid synergistic modified biomass activated carbon prepared by the method is used for pollution treatment of wastewater polluted by refractory organic matters, can greatly reduce pollution of the refractory organic matters to the natural environment, and can be applied to adsorption treatment of wastewater containing methylene blue and perfluorooctanoic acid; and the actual adsorption capacities of methylene blue and perfluorooctanoic acid respectively reach 747 mg / g and 515 mg / g.

Description

Technical Field

[0001] This invention belongs to the technical field of using adsorbents to treat water pollution caused by recalcitrant organic pollutants, and more specifically relates to a method for preparing and applying alkali-acid synergistic modified biomass activated carbon. Background Technology

[0002] With the rapid development of the textile industry, the continuous discharge of textile wastewater has led to increasingly serious water pollution problems, further exacerbating the water shortage crisis. Textile dyeing and printing wastewater, especially methylene blue and perfluorooctanoic acid (PFOA), are two typical recalcitrant organic pollutants that pose a serious threat to water safety. Due to their stable chemical structure and physical properties, these pollutants exhibit strong persistence and bioaccumulation in the environment, and have long-term negative impacts on ecosystems and human health. Therefore, developing efficient technologies for removing these recalcitrant pollutants has become a critical issue that urgently needs to be addressed.

[0003] Currently, many technologies have been used to treat wastewater containing recalcitrant organic pollutants, such as advanced oxidation, biological treatment, and adsorption. Compared with other technologies, adsorption is considered a low-cost, efficient, and easy-to-operate treatment strategy. Among the many materials used for the adsorption of recalcitrant pollutants, carbon-based materials (such as activated carbon, graphene, covalent organic frameworks, metal-organic frameworks, and porous organic polymers) have shown outstanding performance due to their excellent adsorption properties. Lotus leaf stalk activated carbon, as a carbon-based material derived from waste biomass, can effectively reduce preparation costs while also reducing the environmental impact of biological waste, achieving "waste-to-waste" treatment and thus achieving the dual goals of resource conservation and environmental protection.

[0004] Therefore, there is an urgent need in this field for an adsorbent for recalcitrant organic pollutants that is simple to prepare and highly efficient. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing and applying alkali-acid synergistic modified biomass activated carbon, in order to solve the problems existing in the prior art and achieve a simple and efficient preparation method for adsorbents of recalcitrant organic pollutants.

[0006] To achieve the above objectives, the present invention provides the following solution:

[0007] One of the technical solutions of this invention is to provide a method for preparing alkali-acid synergistic modified biomass activated carbon, comprising the following steps:

[0008] Biochar was prepared by carbonization using lotus leaf stalks as raw material; the biochar was then subjected to high-temperature activation with potassium hydroxide and hydrothermal activation with phosphoric acid in sequence to prepare the alkali-acid synergistic modified biomass activated carbon.

[0009] Furthermore, the lotus stems are further subjected to drying, crushing and sieving steps before use; the sieve used for sieving has an aperture of 120 mesh.

[0010] Preferably, the carbonization is carried out under a nitrogen atmosphere, the nitrogen flow rate is 100~120mL / min; the carbonization temperature is 500~800℃, the heating rate is 10~20℃ / min, and the holding time is 2~4h.

[0011] The carbonization temperature described in this invention is 500~800℃. Since lotus stems contain a large amount of organic impurities, a lower carbonization temperature will prevent these impurities from being fully pyrolyzed and volatilized, while a higher carbonization temperature will not effectively preserve the rich functional groups inherent in the biomass.

[0012] Preferably, the potassium hydroxide high-temperature activation includes: mixing the biochar and potassium hydroxide, and performing high-temperature activation to obtain potassium hydroxide high-temperature activated carbon.

[0013] Preferably, the mass ratio of biochar to potassium hydroxide is 1:1 to 1:5; the high-temperature activation is carried out under a nitrogen atmosphere, the flow rate of the nitrogen is 50 to 120 mL / min; the high-temperature activation temperature is 600 to 900℃, the heating rate is 10 to 20℃ / min, and the holding time is 2 to 4 h.

[0014] The mass ratio of biochar to potassium hydroxide in this invention is 1:1 to 1:5. A higher mass ratio of biochar to potassium hydroxide leads to poor pore formation and uneven distribution of active functional groups. A lower mass ratio results in pore collapse and reduced specific surface area during high-temperature activation. The nitrogen flow rate is 50-120 mL / min. A slow nitrogen flow rate can cause impurities to remain in the high-temperature pyrolysis process, leading to secondary reactions. A suitable nitrogen flow rate helps reduce experimental deviations and lower preparation costs. The high-temperature activation temperature is 600-900℃. Excessive activation temperature will damage the inherent pore structure of the lotus stem biochar, while insufficient temperature will result in incomplete reaction and a decrease in pore formation rate. The heating rate is 10-20℃ / min. A rapid heating rate can lead to incomplete pyrolysis of organic impurities and insufficient reaction of potassium hydroxide, resulting in poor pore formation. The heat preservation time is 2-4 hours. If the heat preservation time is too long in the high temperature environment of 600-900℃, it is easy to cause excessive pore formation and collapse of the carbon skeleton, which will affect the subsequent phosphoric acid activation effect.

[0015] Preferably, the high-temperature activation process further includes acid washing, water washing, and drying steps.

[0016] Preferably, the phosphoric acid hydrothermal activation includes: mixing the potassium hydroxide high-temperature activated activated carbon and the phosphoric acid aqueous solution, and performing hydrothermal activation to obtain the alkali-acid synergistic modified biomass activated carbon.

[0017] Preferably, the mass fraction of the phosphoric acid aqueous solution is 40-60%; the hydrothermal activation temperature is 180-220℃, the pressure is 2-3 MPa, and the time is 6-12 h.

[0018] The phosphoric acid aqueous solution described in this invention has a mass fraction of 40-60%. Too high a mass fraction will result in a viscous liquid contaminating the pores of the potassium hydroxide-activated carbon at high temperature. Too low a mass fraction will lead to poor phosphoric acid corrosion of the carbon skeleton. A reasonable phosphoric acid mass fraction can effectively generate more micropores on the mesoporous skeleton. The hydrothermal activation temperature is 180-220℃. Too low a temperature will slow down the reaction rate between phosphoric acid and the carbon precursor, limiting pore formation and surface modification, resulting in insufficient activated carbon performance. Too high a temperature will cause pore wall collapse or pore merging, reducing the micropore ratio, decreasing surface acidity and chemisorption capacity, and affecting the selectivity of activated carbon for polar pollutants. The pressure is 2-3 MPa. Too low a pressure will lead to incomplete reaction or a slow reaction rate, thus affecting pore formation, resulting in an undesirable pore structure and low porosity. The hydrothermal activation time is 6-12 hours. Too short a reaction time will prevent the pore structure from fully forming, reducing the overall pore volume and pore size distribution.

[0019] Preferably, the hydrothermal activation process further includes water washing and drying steps.

[0020] The potassium hydroxide described in this invention needs to be acid-washed and water-washed after high-temperature activation. The purpose of acid washing is to dissolve the potassium salt generated during the high-temperature activation of potassium hydroxide in the activated carbon channels, and further remove the impurity salts generated by ultrapure water. The phosphoric acid needs to be water-washed after hydrothermal activation in order to avoid errors in adsorption performance caused by incomplete washing of phosphoric acid.

[0021] This invention uses potassium hydroxide as a chemical activator. Under high temperature, through the chemical reaction and physical etching effects of the activator, activated carbon acquires excellent physical and chemical properties. Potassium hydroxide activation significantly increases the specific surface area of ​​activated carbon, providing a large number of adsorption sites; it generates abundant micropores (<2nm) and mesopores (2~50nm), improving pore distribution and adapting to the adsorption requirements of different molecular sizes; the activation process also introduces oxygen-containing functional groups, enhancing the adsorption performance for organic pollutants. As a high-temperature activation activator, potassium hydroxide drives the initial pore formation, while the auxiliary effects of metallic potassium and K2CO3 further optimize the pore structure, improving the stability and adsorption performance of activated carbon. The specific reaction process is as follows:

[0022] 6KOH + 2C → 2K2CO3 + 2K + 3H2;

[0023] K₂CO₃ + 2C → 2K + 3CO;

[0024] K2CO3↔2K2O+CO2;

[0025] 2KOH + CO2 → K2CO3 + 3H2O.

[0026] Phosphoric acid hydrothermal activation is a chemical activation method for preparing high-performance activated carbon. Under high-pressure hydrothermal conditions, mild chemical reactions and physical effects can significantly improve the pore structure and surface chemical properties of activated carbon. The high-pressure environment promotes the retention and expansion of volatile gases, restricts gas escape, enhances the expansion effect of the carbon matrix, generates a more uniform and interconnected pore network, accelerates pore formation and the introduction of surface functional groups, and improves adsorption efficiency. Hydrothermal conditions enhance the hydrophilicity of the activated carbon surface, improve its structural stability, reduce the risk of pore collapse, retain the well-developed pore structure and abundant surface chemical groups, and ensure the uniform distribution of functional groups. This process is efficient, mild, and controllable, providing significant advantages for the preparation of high-performance activated carbon.

[0027] Lotus stems possess a well-developed and regular pore structure, which can be well preserved after carbonization. This invention, for the first time, uses lotus stem biochar as a modification material. Utilizing two activation modification methods—high-temperature activation with potassium hydroxide and hydrothermal activation with phosphoric acid—and combining physical and chemical actions during activation, a lotus stem activated carbon with a well-developed pore structure and a surface rich in active functional groups was successfully prepared. Furthermore, lotus stems exhibit good biodegradability in the environment, ensuring that the prepared lotus stem activated carbon aligns with the trend of green environmental protection.

[0028] This invention involves first alkali activation followed by acid activation of biochar prepared from lotus stems. This activation order cannot be reversed because the alkaline activator, potassium hydroxide, reacts more readily with the carbon matrix at high temperatures, generating intermediate products such as K₂CO₃, K₂O, and metallic potassium, accompanied by the release of gases such as CO, CO₂, and H₂. This step, combined with chemical etching and physical expansion, increases the specific surface area of ​​the activated carbon, generating a carbon framework with mesoporous dimensions. Conversely, the acidic activator, under hydrothermal and high-pressure conditions, more easily wets and corrodes the framework. This step, combined with chemical etching and surface purification, generates a microporous structure on the mesoporous carbon framework. Alkali-acid activation before acid activation, compared to acid-acid activation before alkali activation, is more conducive to the formation of a hierarchical pore structure, effectively preparing hierarchical porous activated carbon.

[0029] Many types of activated carbon are currently used to degrade recalcitrant organic pollutants in water. The activated carbon modified from waste lotus stem biomass described in this invention achieves higher adsorption capacity and removal rate at a lower cost compared to adsorbents prepared from other materials (graphene, covalent organic frameworks, metal-organic frameworks, and porous organic polymers, etc.), giving it a significant cost advantage in the removal of recalcitrant organic pollutants. This invention utilizes a synergistic acid-base modification and activation reaction, which is simple and facilitates large-scale production and application, resulting in a substantial cost advantage.

[0030] The second technical solution of the present invention provides alkali-acid synergistic modified biomass activated carbon prepared by the above preparation method.

[0031] The third technical solution of the present invention is to provide the application of the above-mentioned alkali-acid synergistic modified biomass activated carbon in the treatment of water bodies polluted by recalcitrant organic pollutants, wherein the dosage of the alkali-acid synergistic modified biomass activated carbon is 0.2~1 mg / mL.

[0032] The present invention discloses the following technical effects:

[0033] 1. The alkaline-acid synergistic activation modified biomass activated carbon provided by this invention can be used for the pollution treatment of wastewater containing recalcitrant organic pollutants, which can greatly reduce the harm to the natural environment caused by recalcitrant organic pollutants. This invention can be applied to the adsorption treatment of wastewater containing methylene blue and wastewater containing perfluorooctanoic acid. The highest actual adsorption capacity for methylene blue reaches 747 mg / g, and the highest actual adsorption capacity for perfluorooctanoic acid reaches 515 mg / g.

[0034] 2. The method for preparing modified biomass activated carbon by alkali-acid synergistic activation provided by the present invention requires widely available, inexpensive and readily available materials, and the preparation process is simple to operate, has high output, low energy consumption and is environmentally friendly.

[0035] 3. The alkali-acid synergistic activation modified biomass activated carbon provided by this invention has a fast adsorption rate and stable adsorption effect for methylene blue and perfluorooctanoic acid when treating industrial wastewater. It can solve the problems of resource waste and environmental pollution, achieve the goal of "treating waste with waste", and conform to the current concept of green environmental protection and sustainable development. Attached Figure Description

[0036] Figure 1 The flowchart illustrates the preparation process of alkali-acid synergistic activation modified biomass activated carbon according to this invention.

[0037] Figure 2SEM images of lotus stem biochar AC in Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, activated carbon AC-KP modified by synergistic activation of lotus stem with alkali followed by acid in Example 5, and activated carbon AC-PK modified by synergistic activation of lotus stem with acid followed by alkali in Example 6.

[0038] Figure 3 The graph shows the changes in specific surface area, pore size, and pore volume of the lotus stem biochar AC in Example 2, the activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, the activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, the lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5, and the lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6.

[0039] Figure 4 The graphs show the changes in UV absorbance before and after adsorbing methylene blue waste liquid for the following products: lotus stem biomass powder LSP in Example 1, lotus stem biochar AC in Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5, and lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6.

[0040] Figure 5 This is a graph showing the change in UV absorbance of modified lotus stem activated carbon AC-KP before and after adsorption of methylene blue waste liquid in Example 5, where the activated carbon was first activated by alkali and then by acid.

[0041] Figure 6 This is a time-adsorption capacity variation graph of methylene blue for AC-KP modified lotus stem activated carbon, which was activated by synergistic alkali-acid activating process in Example 5.

[0042] Figure 7 The graph shows the time-adsorption capacity of perfluorooctanoic acid (PFOA) on the modified lotus stem activated carbon AC-KP, which was activated by synergistic alkali-acid activating process in Example 5.

[0043] Figure 8 The graph shows the changes in specific surface area and pore volume before and after adsorption of methylene blue and perfluorooctanoic acid by AC-KP modified lotus stem activated carbon in Example 5, which was activated by synergistic alkali-acid activating process. Detailed Implementation

[0044] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0045] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Any stated value or intermediate value within a stated range, as well as each smaller range between any other stated value or intermediate value within said range, is also included within the scope of this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0046] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0047] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be readily apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0048] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0049] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0050] The discarded lotus leaf stems used in this invention were obtained from the Tianmu Lake area near Nanchang Aviation University. Unless otherwise specified, all other raw materials used are commercially available products, and the source of these products does not affect the technical effect of this invention.

[0051] Unless otherwise specified, the room temperature involved in this invention is 25±5℃.

[0052] Example 1 (Preparation method of waste lotus stem biomass powder LSP)

[0053] Waste lotus stems were washed and cut into 2-3 cm pieces, then dried in a high-temperature drying oven at 80°C for 12 hours. The dried lotus stems were then crushed into powder particles by a pulverizer and passed through a 120-mesh sieve to obtain lotus stem biomass powder LSP.

[0054] Example 2 (Preparation method of waste lotus stem biochar AC)

[0055] (1) Place the lotus stem biomass powder in a quartz boat, and place the quartz boat filled with lotus stem powder in a high-temperature tube furnace.

[0056] (2) High-purity nitrogen gas is passed through the device for 25 minutes at a flow rate of 150 mL / min to purge the air from the device;

[0057] (3) The heating rate of the high-temperature tube furnace is set to 10℃ / min, the target temperature is 700℃, the flow rate of high-purity nitrogen is 120mL / min, the holding time is 2h, and lotus stem biochar AC is obtained after heating.

[0058] Example 3 (A method for preparing activated carbon AC-K by high-temperature pyrolysis of potassium hydroxide)

[0059] (1) Weigh 1g of lotus stem biochar AC, keep the mass ratio between lotus stem biochar AC and potassium hydroxide at 1:3, weigh 3g of potassium hydroxide, dissolve the potassium hydroxide in 20mL of deionized water, and then add lotus stem biochar AC.

[0060] (2) Add a magnetic stir bar, set the stirring temperature to room temperature, the speed to 600 r / min, and the stirring time to 12 h, until the potassium hydroxide and lotus stem biochar AC are fully mixed;

[0061] (3) Place it in an oven at 80°C to dry until the mixture becomes viscous. Then transfer it to a quartz boat and place it in a high-temperature tube furnace for high-temperature pyrolysis activation.

[0062] (4) High-purity nitrogen gas was pre-purged for 25 min at a rate of 150 mL / min to purge the air from the high-temperature tube furnace. The high-temperature tube furnace was set to a heating rate of 10 °C / min, a target temperature of 800 °C, a high-purity nitrogen gas flow rate of 120 mL / min, and a holding time of 2 h. The product was collected after heating was completed.

[0063] (5) The collected product was repeatedly washed with a 1% hydrochloric acid solution and deionized water until the pH of the filtrate was 7. The product was then dried at 80°C for 12 hours to obtain potassium hydroxide high-temperature activated carbon AC-K.

[0064] Example 4 (A method for preparing hydrothermally activated carbon AC-P with phosphoric acid)

[0065] (1) Weigh 1g of lotus stem biochar AC, take 12mL of 85% phosphoric acid and add 12mL of deionized water to dilute it to a 45% phosphoric acid solution.

[0066] (2) Transfer a 45% dilute phosphoric acid solution into the inner liner of the reactor and sonicate for 10 min;

[0067] (3) Add 1g of lotus stem biochar AC to a 45% dilute phosphoric acid solution and stir with a glass rod until well mixed;

[0068] (4) Sonicate the reaction vessel containing the mixture for 10 minutes to remove the bubbles generated during the stirring process and make the two fully mixed;

[0069] (5) Place the inner liner of the reactor into the stainless steel reactor. After the oven temperature rises to 200°C, place it into the hydrothermal reaction device and set the heat preservation time to 12h.

[0070] (6) After the reaction is complete, the filtrate is repeatedly washed with deionized water until the pH of the filtrate is 7. After drying the water, the hydrothermal activated carbon AC-P of phosphoric acid is prepared.

[0071] Example 5 (A method for preparing AC-KP activated carbon by high-temperature activation with potassium hydroxide followed by hydrothermal activation with phosphoric acid)

[0072] Same as Example 4, except that the lotus stem biochar AC in step (1) is replaced with an equal mass of potassium hydroxide high-temperature activated carbon AC-K to prepare activated carbon AC-KP that is first activated by potassium hydroxide high temperature and then activated by phosphoric acid hydrothermal.

[0073] Example 6 (A method for preparing activated carbon AC-PK by first hydrothermal activation with phosphoric acid and then high-temperature activation with potassium hydroxide)

[0074] Same as Example 3, except that the lotus stem biochar AC in step (1) is replaced with an equal mass of phosphoric acid hydrothermal activated carbon AC-P to prepare activated carbon AC-PK that is first activated by phosphoric acid hydrothermal activation and then activated by potassium hydroxide high temperature.

[0075] Performance testing:

[0076] 1. SEM analysis:

[0077] The following activated carbons were prepared: lotus stem biochar AC from Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5, and lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6. These samples were then blown onto conductive adhesive using a syringe rubber bulb and adhered to the SEM sample stage. The samples were then sputtered with gold to prevent surface charge accumulation from affecting imaging quality. After being transferred to the sample chamber and evacuated, they were ion sputtered for 30 seconds. The samples were then imaged using a JSM-7800F Prime SEM at magnifications ranging from 25 to 1,000,000 times. The results are as follows: Figure 2 As shown.

[0078] Figure 2SEM images of lotus stem biochar AC in Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, activated carbon AC-KP modified by synergistic activation of lotus stem with alkali followed by acid in Example 5, and activated carbon AC-PK modified by synergistic activation of lotus stem with acid followed by alkali in Example 6. Figure 2 It can be seen that under the high-temperature pyrolysis condition of 700℃, lotus stem biochar AC retains the original macroporous structure of lotus stems relatively well. Activated carbon AC-K with rich mesoporous structure was prepared by pyrolysis of lotus stem biochar AC and potassium hydroxide at a mass ratio of 1:3 at 800℃ for 2 hours. After hydrothermal activation with phosphoric acid, activated carbon AC-K was obtained as AC-KP, which generated more micropores on the basis of the mesoporous structure, further reducing the pore size and optimizing the pore structure distribution of the activated carbon. AC-P, after hydrothermal reaction of lotus stem biochar AC and phosphoric acid, retained the original macroporous structure of AC, but generated fewer mesopores; the pore-forming effect was limited under the mild hydrothermal reaction conditions. AC-PK was prepared by high-temperature pyrolysis activation of AC-P after hydrothermal reaction with potassium hydroxide. The strong alkali etching effect generated mesopores on the basis of the macroporous structure of AC-P, but given the limited pore-forming effect of the previous step, the pore-forming effect of this step was also relatively limited. SEM analysis demonstrated that the pore-forming effect of AC-KP activated carbon modified by alkali followed by acid synergistic activation was better than that of other preparation methods.

[0079] 2. BET Data Analysis:

[0080] 50 mg of each of the following activated carbons were taken: lotus stem biochar AC from Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5, and lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6. The weight of the BET tube used for testing and the total weight after containing the sample were weighed for data input during the program setup process. The specific surface area, pore size, and pore volume of the samples were measured using a Micromeritics® TriStar II instrument. The results are as follows: Figure 3 As shown.

[0081] Figure 3 This is a graph showing the changes in specific surface area, pore size, and pore volume of the following activated carbons: AC (lotus stem biochar) from Example 2, AC-K (activated carbon prepared by high-temperature pyrolysis activation with potassium hydroxide) from Example 3, AC-P (activated carbon prepared by hydrothermal activation with phosphoric acid) from Example 4, AC-KP (activated carbon modified by synergistic activation of lotus stems with alkali followed by acid) from Example 5, and AC-PK (activated carbon modified by synergistic activation of lotus stems with acid followed by alkali) from Example 6. Figure 3As can be seen, the test results are consistent with the SEM image analysis results. In Example 5, the specific surface area of ​​the modified lotus stem activated carbon AC-KP, which was activated by alkali followed by acid, was the largest among the five materials, reaching 2107.7153 m². 2 / g, with the smallest pore size of 2.4541nm and the largest pore volume of 1.144212cm³. 3 / g. BET data analysis further quantified the SEM analysis results, demonstrating that the modified lotus stem activated carbon AC-KP, which was activated by synergistic alkali-acid activation, has a superior pore-forming effect.

[0082] 3. UV-Vis ultraviolet absorption analysis:

[0083] 10 mg of each of the following activated carbons were taken: lotus stem biomass powder LSP from Example 1, lotus stem biochar AC from Example 2, activated carbon AC-K prepared by high-temperature pyrolysis activation with potassium hydroxide in Example 3, activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4, lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5, and lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6. These were added to 50 mL of 150 mg / L methylene blue waste liquid. Both the stock methylene blue solution and the methylene blue solution after 1 hour of water bath shaking adsorption were diluted 25 times and used to compare the changes in absorbance before and after adsorption. The results are as follows: Figure 4 As shown.

[0084] Figure 4 The graph shows the changes in UV absorbance before and after adsorbing methylene blue waste liquid for the following activated carbons: LSP (lotus stem biomass powder) in Example 1, AC (lotus stem biochar) in Example 2, AC-K (activated carbon prepared by high-temperature pyrolysis activation with potassium hydroxide) in Example 3, AC-P (activated carbon prepared by hydrothermal activation with phosphoric acid) in Example 4, AC-KP (activated carbon modified by synergistic activation with alkali followed by acid) in Example 5, and AC-PK (activated carbon modified by synergistic activation with acid followed by alkali) in Example 6. Figure 4 It can be seen that the characteristic peak of methylene blue was obtained at a wavelength of 663 nm, which was used to characterize the change of methylene blue concentration during the adsorption process. The lotus stem biochar AC in Example 2 and the activated carbon AC-P prepared by hydrothermal activation with phosphoric acid in Example 4 had no adsorption effect on methylene blue. The lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5 had the best adsorption effect on methylene blue, which was better than the activated carbon AC-K prepared by high temperature pyrolysis activation with potassium hydroxide in Example 3, better than the lotus stem activated carbon AC-PK modified by synergistic activation with acid followed by alkali in Example 6, and better than the lotus stem biomass LSP in Example 1.

[0085] Further adsorption studies were conducted on methylene blue using the modified lotus stem activated carbon AC-KP, which underwent synergistic activation with alkali followed by acid, as described in Example 5. The results are as follows... Figure 5 As shown.

[0086] Figure 5 This is a graph showing the change in UV absorbance before and after adsorption of methylene blue waste liquid by AC-KP activated carbon modified from lotus stems using a combination of alkali and acid synergistic activation in Example 5. Figure 5 It can be seen that methylene blue at a concentration of 150 mg / L reaches adsorption saturation in 30 min, and the ultraviolet absorbance is close to 0. The color change of the solution during the test can also be observed. After adsorption, the solution gradually becomes transparent, indicating that the methylene blue in the water is completely removed.

[0087] 4. Methylene blue adsorption capacity analysis:

[0088] 10 mg of the modified lotus stem activated carbon AC-KP (activated by synergistic alkali-acid activating process as described in Example 5) was weighed and added to 50 mL of 150 mg / L methylene blue waste liquid. 1 mL of the original methylene blue solution and 1 mL of the waste liquid after adsorption at different times from 0 to 1440 min were taken and diluted 25 times. The colorimetric tube containing the diluted solution was sonicated for 10 min, and then UV-Vis ultraviolet absorption was measured using a Shimadzu UV-1900i. A standard curve was obtained by plotting the ultraviolet absorbance at different concentrations. The methylene blue concentration corresponding to the ultraviolet absorbance at different times was calculated from the standard curve. Finally, the adsorption capacity change of the adsorbent at different times was calculated. The results are as follows: Figure 6 As shown.

[0089] Figure 6 This is a time-adsorption capacity variation graph of methylene blue for AC-KP activated carbon modified from lotus stems through synergistic activation with alkali followed by acid in Example 5. Figure 6 It can be seen that, in Example 5, the adsorption capacity of the lotus stem activated carbon AC-KP, which was synergistically activated by alkali followed by acid, increased significantly within 0-5 minutes, reaching adsorption saturation at 30 minutes, with a removal rate of over 99% for methylene blue. The methylene blue adsorption capacity analysis results indicate that the lotus stem activated carbon AC-KP, synergistically activated by alkali followed by acid in Example 5, exhibits a rapid adsorption rate, high adsorption capacity, and a removal rate approaching 100% for methylene blue.

[0090] 5. Perfluorooctanoic acid adsorption capacity analysis:

[0091] To further verify the removal capacity of the modified lotus stem activated carbon AC-KP, which was activated by alkali followed by acid in Example 5, for other recalcitrant organic pollutants, perfluorooctanoic acid (PFOA) was selected as the pollutant and its adsorption performance was studied.

[0092] 10 mg of the modified lotus stem activated carbon AC-KP (pre-alkali followed by acid synergistic activation) from Example 5 was weighed and added to 50 mL of 100 mg / L perfluorooctanoic acid (PFOA) waste solution. 1.5 mL of the PFOA stock solution and 1.5 mL of the post-adsorption waste solution collected at different time points from 0 to 1440 min were directly added to sample vials. The integral areas of the characteristic peaks at different time points were measured using a Waters Xevo G2-XS QTof LC-MS / MS. A standard curve was plotted using the integral areas of the corresponding characteristic peaks at different concentrations. The integral areas of the characteristic peaks were then converted to the PFOA concentration from the standard curve, and the adsorption capacity variation of the adsorbent at different time points was calculated. The results are as follows: Figure 7 As shown.

[0093] Figure 7 This is a time-adsorption capacity graph of perfluorooctanoic acid (PFOA) for the modified lotus stem activated carbon AC-KP, which underwent synergistic activation with prior alkali followed by acid in Example 5. Figure 7 It can be seen that the adsorption capacity of the modified lotus stem activated carbon AC-KP, which was activated by alkali followed by acid in Example 5, increased significantly within 0-60 min, reaching adsorption saturation at 120 min, and reaching the maximum adsorption capacity of 515 mg / g at 1440 min, with a removal rate of 85%. The perfluorooctanoic acid (PFOA) adsorption capacity analysis shows that the modified lotus stem activated carbon AC-KP, activated by alkali followed by acid in Example 5, has a good adsorption effect on PFOA, and combined with its low cost advantage, it has great application potential.

[0094] 6. BET data analysis after adsorption of methylene blue and perfluorooctanoic acid:

[0095] The samples after adsorption of methylene blue and perfluorooctanoic acid by the modified lotus stem activated carbon AC-KP (calcified with alkali followed by acid in Example 5) were compared with the samples before adsorption using BET data analysis. The results are as follows: Figure 8 As shown.

[0096] Figure 8 This is a graph showing the changes in specific surface area and pore volume before and after adsorption of methylene blue and perfluorooctanoic acid by AC-KP activated carbon modified from lotus stems in Example 5, synergistically activated with alkali followed by acid. Figure 8 It can be seen that the specific surface area increased from 2107.7153 m² after methylene blue adsorption. 2 / g decreased to 268.994m 2 / g, pore volume is 1.144212cm³ 3 / g decreased to 0.16444cm 3 / g, the specific surface area after adsorption of perfluorooctanoic acid increased from 2107.7153m². 2 / g decreased to 738.9905m 2 / g, pore volume is 1.144212cm³ 3 / g decreased to 0.41121cm3 The / g indicates that the two types of recalcitrant organic pollutants were effectively anchored in the activated carbon adsorbent after adsorption, resulting in a significant decrease in the specific surface area and pore volume of the activated carbon. BET data analysis after adsorption of methylene blue and perfluorooctanoic acid (PFOA) shows that the lotus stem activated carbon AC-KP modified by synergistic activation with alkali followed by acid in Example 5 can effectively adsorb these two recalcitrant organic pollutants and anchor them on the adsorbent surface.

[0097] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0098] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing alkali-acid synergistic modified biomass activated carbon, characterized in that, Includes the following steps: Using lotus leaf stalks as biomass raw material, biochar was prepared by carbonization; the biochar was then subjected to high-temperature activation with potassium hydroxide and hydrothermal activation with phosphoric acid in sequence to prepare the alkali-acid synergistic modified biomass activated carbon.

2. The preparation method according to claim 1, characterized in that, The carbonization is carried out under a nitrogen atmosphere, with a nitrogen flow rate of 50-120 mL / min; the carbonization temperature is 500-800℃, the heating rate is 10-20℃ / min, and the holding time is 2-4 h.

3. The preparation method according to claim 1, characterized in that, The potassium hydroxide high-temperature activation includes: mixing the biochar and potassium hydroxide, and then performing high-temperature activation to obtain potassium hydroxide high-temperature activated carbon.

4. The preparation method according to claim 3, characterized in that, The mass ratio of biochar to potassium hydroxide is 1:1 to 1:

5. The high-temperature activation is carried out under a nitrogen atmosphere with a nitrogen flow rate of 50 to 120 mL / min. The high-temperature activation temperature is 600 to 900°C, the heating rate is 10 to 20°C / min, and the holding time is 2 to 4 hours.

5. The preparation method according to claim 3, characterized in that, The high-temperature activation process also includes acid washing, water washing, and drying steps.

6. The preparation method according to claim 3, characterized in that, The phosphoric acid hydrothermal activation includes: mixing the potassium hydroxide high-temperature activated activated carbon and the phosphoric acid aqueous solution, and performing hydrothermal activation to obtain the alkali-acid synergistic modified biomass activated carbon.

7. The preparation method according to claim 6, characterized in that, The mass fraction of the phosphoric acid aqueous solution is 40-60%; and / or the hydrothermal activation temperature is 180-220℃, the pressure is 2-3MPa, and the time is 6-12h.

8. The preparation method according to claim 6, characterized in that, The hydrothermal activation process also includes water washing and drying steps.

9. Alkali-acid synergistic modified biomass activated carbon prepared by the preparation method according to any one of claims 1 to 8.

10. The application of the alkali-acid synergistic modified biomass activated carbon according to claim 9 in the treatment of water bodies polluted by recalcitrant organic pollutants, characterized in that, The dosage of the alkali-acid synergistic modified biomass activated carbon is 0.2~1 mg / mL.

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